Parks's versatility and supple prose is again manifested in his sixth novel, his second foray into the psychological suspense genre (though this work has neither the mesmerizing narrative voice nor the taut pacing of the praised Juggling with the Stars .) Here he uses geological metaphors to delineate the moral and emotional conflicts of his characters--``shear'' being the way a quarried rock may expand and break after enormous stresses are released. Sent to Italy to investigate the death of a quarry employee, geologist Peter Nicholson receives bribes of cash and sex from Thea, daughter of the firm's wily boss, and is told to write a report exonerating the company. Marrried and a father, Nicholson feels his body's texture fatally vulnerable to his own ``shear.'' Though he has brought along his mistress, 18-year-old Margaret, he nonetheless succumbs to Thea's seduction. His pregnant wife faxes him from England, threatening an abortion. The dead man's widow and child show up with a shard of blood-stained rock. In this area of the world, rock is ubiquitous-- in door and window sills, basins, stairs, cobblestones. Grimly introspective, Nicholson is haunted by the arid volcanic landscape and the ``evil in the rock'' which infects his foes and himself. Only ``his pearl'' Margaret (a play on the etymology of her name) remains free of taint, pearls being organic rather than mineral. Events turn sinister, while the tale takes on mythic resonance from the region's ancient gods--Theseus, Neptune, Pandora. Unfortunately, some of the technical analyses of rock components are turgid, but the tale's horrific denouement proves memorable. (July)